1. Field of the Invention
This invention relates to an automatic apparatus for measuring bores and other objects to be measured.
2. Description of the Related Art
A coordinate measuring instrument is known as an apparatus which moves its touch probe toward a three-dimensional object to measure any point on the object and then processes the measured data.
The coordinate measuring instruments can be categorized, by its operation type, into a manual type, a motor-drive type, a CNC (Computer Numerical Control) type and the like.
By the way, such a high precision conventional coordinate measuring instrument is generally placed in a special room, usually separate from a production line for the objects, in which the temperature and the humidity are kept constant. It is therefore necessary for an operator to pick up and bring one object from the production line into the room for measurement.
According to the recent necessity of effective production, it is desired to provide a coordinate measuring instrument which may be set on the production line, so-called for an in-line measurement. The in-line measurement should have a capability of producing a fast and automatic measurement so as to not slow down the production speed.
On the contrary, the present coordinate measuring instrument needs to process three points of data for an inner diameter measurement of a bore by using its probe. The three data points may be used for define the center of the bore, but which is not ideal for a fast measurement of the inner diameter. And, the diameter may be processed with reference to a rather distant origin for the measurement, so that the accuracy of the measurement is likely to be bad.
It is often the case in in-line measurement devices to measure only the size of the bores, wherein the function to define the center position of the bore is just an un-wanted one.
While, as one of inner diameter measuring devices, there are well-known manual hole-testers, for example those described in Japanese Patent Application Publication No. 63-4641 and Japanese Utility-model Application Laid-open No. 60-41811 and others. But these should be used manually, so that the operation efficiency may not be high especially in cases where many diameters exist and face have a different diameter.
The inventors have noted that in 70 to 80 percent of the incidents where objects are to be measured, the measurements of bores are not for the purpose of providing a center point and the distance between two of them but for the inner diameter.
Accordingly, in this field, it is desired to provide an instrument which may effectively measure the inner diameter of the bores, if necessary.
An object of the present invention is to provide an automatic inner diameter measuring apparatus capable of providing a fast measurement of an inner diameter and being used in an in-line measurement situation.
Another object is to provide a method of providing a fast zero adjustment of the automatic inner diameter measuring apparatus.